Waterproof garments, such as oil skins, have been known for many years. Whilst these protect the wearer against water penetration, they are uncomfortable to wear since they are unable to allow perspiration from the body to escape, so that the inside of the garment becomes clammy. More recently, fabrics have become available which resist the ingress of liquid water, yet at the same time allow water vapour to pass through. One such fabric is available under the trademark GORE-TEX and comprises an expanded porous Polytetrafluoroethylene (PTFE) membrane. Typically, the fabric comprises a porous expanded PTFE membrane laminated to a woven fabric (typically nylon or polyester) which protects the outside of the membrane. GORE-TEX fabric is generally a three-layer construction which further includes an open knitted material laminated to the inside of the porous expanded PTFE membrane, which protects the membrane and improves the feel of the fabric. The fabric is used to produce waterproof breathable garments in substantially conventional manner. However, in order to prevent water penetration at the seams of the garment, it is normal to apply a heat bonded tape over the inside of the seams. The heated tape is applied under pressure to the seam, such that the melted adhesive penetrates the inner knitted layer of the fabric and bonds to the PTFE membrane itself, thereby sealing the seam against water penetration.
Waterproof breathable garments find application in a variety of fields, including industrial clothing, leisure clothing and military clothing. A wide variety of garments may be produced, including socks, mitts, jackets, suits, trousers, overalls, bib-and-brace overalls etc. However, one particularly important application is in the construction of aviation survival suits termed Over Water Flying Suits (OWFS). These suits are worn by pilots and passengers undertaking over water flights, such as Air Force Personnel and Crews servicing offshore installations such as oil rigs.
It is a requirement that over water flying suits be washed and tested for water tightness every week or two during use. The OWFS must be capable of keeping dry a person who has accidentally come down in the sea for a period of at least half an hour. This is important in cold Northern seas in order to prevent hypothermia prior to rescue. One test standard prescribes a maximum of 100 grams of water ingress over a 20 minute period. Since the flight suits become chaffed, worn or torn in use, or the taped seams fail, regular testing is necessary.
One test method is to turn the flight suit inside out and fill it with water, and observe any signs of leakage. This is a cumbersome and time consuming method, which moreover may damage the suits due to the weight of water inside.
At present, flying suits are conventionally tested by inflating the suit with air, applying soapy water to the outside of the suit and looking for any tell-tale bubbles. Any leaks are marked and then sealed with tape. This method is also time consuming and therefore costly. Moreover, the method detects air leaks rather than water leaks. Thus, there may be pin holes which allow air through but which would not allow liquid water through and therefore would not jeopardise the waterproofness of the fabric. In other words, this test method results in more repair work being carried out than is necessary. Also the application of unnecessary sealing tape is undesirable since it tends to increase the rigidity of the flying suits and lessens the breathability, so that they become more uncomfortable to wear; and areas adjacent pieces of repair tape tend to be more liable to failure through chaffing.
It is an object of the present invention to provide a test procedure which mitigates these problems.